1. Updated CpuFlushTlb() according to IA-64 programmer's guide

2. Updated Thunk code to preserve EFLAGS/RFLAGS across real mode code invocation
3. Updated comments in x86Thunk.c

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@248 6f19259b-4bc3-4df7-8a09-765794883524

MdePkg/Library/BaseLib/x86Thunk.c

@@ -95,6 +95,10 @@ AsmGetThunk16Properties (
   ASSERT (ExtraStackSize != NULL);
 
   *RealModeBufferSize = m16Size;
+
+  //
+  // Extra 4 bytes for return address, and another 4 bytes for mode transition
+  //
   *ExtraStackSize = sizeof (IA32_DWORD_REGS) + 8;
 }